To date, tobacco science has revealed little about the natural history of continued smoking and quitting, apart from abstinence rates and ultimate disease outcomes. Tracking the fates of smokers who succeed or fail in a quitattempt promises to uncover new correlates of cessation in important physiological and psychosocial domains and may reveal the mechanisms by which important outcomes (e.g., atherosclerosis, improved quality of life [QOL]) occur. A longitudinal approach that tracks smoking behavior over an extended period may also identify factors that precipitate late relapse. This study will follow 360 successful quitters and 540 continuing smokers for three years after a quit attempt to track smoking behavior, atherosclerotic progression, psychiatric symptoms, QOL, social networks, physical activity, alcohol use/abuse, and other variables. Analyses will contrast quitters and continuing smokers on these variables. Medical and psychosocial constructs will be measured by multiple indicators to obtain convergent validity. We hypothesize that successful cessation will be associated with arrest of atherosclerosis, reduced psychiatric diagnoses and symptoms, enhanced QOL, and reduced alcohol intake. We also expect that some quitters (e.g., those who gain considerable weight) will experience negative outcomes, such as hypedipidemia, hypertension, and reduced QOL. We will explore relations of individual differences, including genetic differences, with quitting correlates and mediational variables. Analyses will also test the ability of social factors (e.g., exposure to smokers, social support) and alcohol use to account for relapses occurring after one year of abstinence. Data gathered in this study should reveal and enhance our understanding of positive effects of quitting in physiological and psychosocial domains. Educating smokers about such benefits may motivate more smokers to quit. Additionally, uncovering adverse events associated with cessation may help smokers avoid such outcomes and identify targets for risk-reduction interventions, including interventions to prevent late relapse.